U.S. patent number 7,312,445 [Application Number 11/105,669] was granted by the patent office on 2007-12-25 for pyramid-shaped near field probe using surface plasmon wave.
This patent grant is currently assigned to Samsung Electro-Mechanics Co., Ltd.. Invention is credited to Ho Seop Jeong, Anatoliy Lapchuk, Dong Ik Shin.
United States Patent |
7,312,445 |
Lapchuk , et al. |
December 25, 2007 |
Pyramid-shaped near field probe using surface plasmon wave
Abstract
Disclosed herein is a pyramid-shaped near field probe which
forms and changes a near field at the aperture of the probe. The
pyramid-shaped near field probe of the present invention includes a
probe body and metal films. The probe body is constructed in the
form of a pyramid using a semiconductor process using a dielectric
member and receives an electromagnetic wave. The metal films are
symmetrically coated on two predetermined sides of four sides of
the probe body while being spaced apart from each other. The
pyramid-shaped near field probe allows a surface plasmon wave
induced on the surfaces of the metal films due to the
electromagnetic wave to progress to the aperture of the probe body
through the boundary surface between the probe body and the metal
films.
Inventors: |
Lapchuk; Anatoliy (Kyeonggi-do,
KR), Jeong; Ho Seop (Kyeonggi-do, KR),
Shin; Dong Ik (Kyeonggi-do, KR) |
Assignee: |
Samsung Electro-Mechanics Co.,
Ltd. (Kyunggi-do, KR)
|
Family
ID: |
36144318 |
Appl.
No.: |
11/105,669 |
Filed: |
April 13, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060076474 A1 |
Apr 13, 2006 |
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Foreign Application Priority Data
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Oct 11, 2004 [KR] |
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10-2004-0080876 |
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Current U.S.
Class: |
250/306;
G9B/7.126; 369/13.33 |
Current CPC
Class: |
G01Q
60/22 (20130101); B82Y 10/00 (20130101); G11B
7/1387 (20130101); B82Y 20/00 (20130101); B82Y
35/00 (20130101); G01Q 80/00 (20130101) |
Current International
Class: |
G01B
11/00 (20060101) |
Field of
Search: |
;250/234,306,307
;369/126,13.33 ;385/15,146 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Korean Patent Abstracts for 1020030044141 A published on Jun. 9,
2003. cited by other.
|
Primary Examiner: Epps; Georgia
Assistant Examiner: Ko; Tony
Attorney, Agent or Firm: Darby & Darby P.C.
Claims
What is claimed is:
1. A near field probe, comprising: a dielectric member formed in a
pyramid shape having an aperture to receive an electromagnetic
wave; and metal films symmetrically coated on two predetermined
sides of the dielectric member while being spaced apart from each
other, wherein said probe is operable to allow a surface plasmon
wave induced on surfaces of the metal films to propagate to the
aperture through boundary surfaces between the dielectric member
and the metal films.
2. The near field probe according to claim 1, wherein the metal
films are formed having an area smaller than the sides of the
dielectric member.
3. The near field probe according to claim 1, wherein at least one
of the metal film ends are eliminated from an aperture region of
the dielectric member.
4. The near field probe according to claim 3, wherein the aperture
region of the dielectric member is designed to allow only a
waveguide mode of TM00 to be formed therein by a surface plasmon
wave propagating through the metal film.
5. The near field probe according to claim 3, wherein the metal
film end is eliminated by an etching process.
6. The near field probe according to claim 1, wherein the
dielectric member is at least one of a glass and a glass-related
member.
7. The near field probe according to claim 1, wherein the metal
films symmetrically coated on the two sides of the dielectric
member are conductive materials.
8. The near field probe according to claim 1, wherein the
symmetrically coated metal films cause a potential difference
therebetween when a surface plasmon wave propagates to the aperture
region of the dielectric member through a boundary surface between
the dielectric member and the metal films.
Description
INCORPORATION BY REFERENCE
The present application claims priority under 35 U.S.C. .sctn.119
to Korean Patent Application No. 2004-80876 filed on Oct. 11, 2004.
The content of the application is incorporated herein by reference
in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to pyramid-shaped near
field probes using surface plasmon waves and, more particularly, to
a near field probe, which forms and changes a near field at the
aperture of the probe using a surface plasmon wave propagating
through the boundary surface between a probe body made of a
dielectric and metal films symmetrically coated on the sides of the
probe body.
2. Description of the Related Art
Generally, in order to store a greater amount of information per
unit area in an optical information storage device, the wavelength
of a recording light source must be reduced or the numerical
aperture of a condensing lens must be increased. In the case of
wavelength, a blue laser diode may be developed, and in the case of
numerical aperture, a maximum of 1.0 may be obtained.
However, such an optical information storage scheme is limited in
recording high density information in an advanced information
storage device requiring high density recording due to the
refractive limit of light, etc.
For alternative technology for overcoming the above limitation,
Scanning Probe Recording (SPR) technology using the probe of an
Atomic Force Microscope (AFM), super resolution media technology,
technology using a near field probe overcoming the refractive limit
of light, etc. have been developed. In particular, a near field
probe using an optical fiber has been developed.
With reference to FIGS. 1 to 5, the construction and operation of a
near field probe using an optical fiber is described.
As shown in FIGS. 1 and 2, an optical fiber 10 used for a near
field probe includes a core 11 for guiding externally incident
light, and a cladding 12 surrounding the core 11 to protect the
core 11.
In this case, the core 11 is made of quartz glass with a diameter
of 10 .mu.m and plastic material, and the cladding 12 is made of
glass material having a refractive index differing from that of the
core 11.
A process of forming a probe on the optical fiber 10 having the
above construction is described below.
As shown in FIG. 3, after one end of the core 11, not heated, is
firmly held using a mechanism while heat is applied to the other
end thereof at a certain temperature or above and the other end is
heated, the heated portion is pulled using a mechanism, so that a
conical optical fiber 14 having an aperture 13 is formed.
In this case, the aperture 13 is preferably formed to cause the
diameter thereof to be about 0.05 to 0.3 .mu.m. If the aperture 13
is formed in this way, the size of a near field formed at the
aperture 13 due to the light transmitted through the conical
optical fiber 14 is about 100 nm or less.
As described above, after the conical optical fiber 14 is formed
through a pulling process, a metal, such as aluminum, is coated to
form a metal layer 15 on an external surface of the conical optical
fiber 14 as shown in FIG. 4, so that an optical fiber probe 16
using the optical fiber is completely produced.
However, the above-described optical fiber probe 16 using the
optical fiber is disadvantageous in that, if a traveling wave 20
propagates into the conical optical fiber 14 and reaches a region
near a diameter having a size similar to the wavelength of the
traveling wave while propagating into the optical fiber 14, as
shown in FIG. 5, the progression of light is difficult, so that the
intensity of the traveling wave 20 decreases sharply.
At this time, in order to obtain the information on spatial
resolution below the wavelength, the diameter of the aperture 13 of
the optical fiber probe 16 must be smaller than the wavelength of
the traveling wave 20. Therefore, as the traveling wave 20
approaches the aperture 13, the traveling wave 20 almost
disappears, and only an evanescent wave 21, losing traveling
characteristics, exists in the region of the aperture 13 of the
optical fiber probe 16.
At this time, the intensity of the evanescent wave 21 existing near
the aperture 13 of the optical fiber probe 16 decreases to 0.01% or
less of the intensity of incident light. For a method of solving
the above disadvantage, a metal film functioning to allow light
with a size below the refractive limit to pass through the optical
fiber 14 as well as to prevent light guided through the conical
optical fiber 14 from leaking to the outside is coated on the
external surface of the optical fiber 14.
However, since the optical fiber probe using an optical fiber
constructed as described above has extremely low transmissivity, it
has limitations in Signal-to-Noise (S/N) ratio and recording and
reproducing speed, so that the optical fiber probe causes a great
number of problems when it is used for a high density optical
recording apparatus.
Further, the above-described optical fiber probe using an optical
fiber is problematic in that, since light guided to the aperture
region is basically formed to have multiple modes, such as traverse
magnetic modes TM.sub.00, TM.sub.10 and TM.sub.20, it is difficult
to form a sharp beam spot on the aperture.
Further, the optical fiber probe using an optical fiber is
problematic in that, since it is manufactured in such a way that,
after heat processing is executed for the optical fiber, a conical
optical fiber is formed by a pulling operation, and a metal film is
coated on the conical optical fiber, it is difficult to
structurally manufacture the optical fiber probe.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind
the above problems occurring in the prior art, and an object of the
present invention is to provide a pyramid-shaped near field probe,
which propagates a surface plasmon wave through metal films
symmetrically coated on sides of a pyramid-shaped probe body, thus
forming a near field at the aperture of the probe.
In order to accomplish the above object, the present invention
provides a pyramid-shaped near field probe using a surface plasmon
wave, comprising a dielectric member formed in a pyramid shape to
receive an electromagnetic wave; and metal films symmetrically
coated on two predetermined sides of four sides of the dielectric
member while being spaced apart from each other, wherein the probe
allows a surface plasmon wave induced on surfaces of the metal
films due to the electromagnetic wave to progress to a region of an
aperture of the dielectric member through a boundary surface
between the dielectric member and the metal films.
In this case, the present invention allows only a waveguide mode of
TM.sub.00 to exist at the aperture of the dielectric member by
eliminating the end of any one of the metal films that are
symmetrically coated on two predetermined sides of four sides of
the dielectric member while being spaced apart from each other.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and other advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a perspective view showing an optical fiber used for a
conventional optical fiber probe;
FIG. 2 is a sectional view showing the optical fiber used for the
conventional optical fiber probe;
FIG. 3 is a side view showing an optical fiber probe formed by a
pulling process for an optical fiber;
FIG. 4 is a perspective view of a conventional optical fiber probe
on which a metal film is coated to prevent the attenuation of an
optical signal propagating through an optical fiber;
FIG. 5 is a perspective view of a conventional optical fiber probe
to show the change in a traveling wave that propagates through the
optical fiber probe;
FIG. 6 is a perspective view showing the construction of a
pyramid-shaped probe body formed by a semiconductor process
according to the present invention;
FIG. 7 is a perspective view showing the construction of a
pyramid-shaped near field probe according to an embodiment of the
present invention;
FIG. 8 is a perspective view showing the construction of a
pyramid-shaped near field probe in which an end of a metal film is
cut according to another embodiment of the present invention;
FIG. 9 is a sectional view showing the construction of a
pyramid-shaped near-field probe in which an end of a metal film is
cut according to a further embodiment of the present invention;
FIGS. 10a and 10b are views showing the shape of a beam spot formed
in the aperture region of the pyramid-shaped near field probe
according to the present invention; and
FIG. 11 is a view showing the construction of an optical
information recording and reproducing apparatus to which the
pyramid-shaped near field probe of the present invention is
applied.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described
in detail with reference to the attached drawings.
Reference now should be made to the drawings, in which the same
reference numerals are used throughout the different drawings to
designate the same or similar components.
With reference to FIGS. 6 to 8, the construction and manufacturing
process of a pyramid-shaped near field probe according to the
present invention are described in detail.
The near field probe of the present invention allows a surface
plasmon wave to propagate to the end of the probe through metal
films symmetrically coated on the sides of a pyramid-shaped probe
body, thus forming a near field. As shown in FIGS. 6 to 8, the
pyramid-shaped near field probe includes a pyramid-shaped probe
body 110 and metal films 120.
The probe body 110, which functions to guide electromagnetic waves
that are incident from an external light source and include
predetermined waveguide modes, for example, TM.sub.00, TM.sub.10
and TM.sub.20 modes, is constructed in the form of a pyramid having
both ends open and rectangular, by a semiconductor process using a
predetermined dielectric member.
In order to store a greater amount of information per unit area in
a predetermined optical information storage device, only an
electromagnetic wave having a waveguide mode of TM.sub.00 must be
output to the region of the aperture 111 of the probe body 110. For
this operation, the electromagnetic wave having an electric field
smaller than the diameter of one end of the probe body 110 is
allowed to be incident on the probe body 110, thus enabling only
the electromagnetic wave having a waveguide mode of TM.sub.00 to be
output to the region of the aperture 111 of the probe body 110.
However, if an electromagnetic wave having an electric field
greater than the diameter of one end of the probe body 110, on
which the electromagnetic wave is incident, the electromagnetic
wave having a waveguide mode of TM.sub.20 is output to the aperture
region 111 of the probe body 110. However, if the electromagnetic
wave having a waveguide mode of TM.sub.20 does not coincide with
the center of one end of the probe body 110, an electromagnetic
wave having a waveguide mode of TM.sub.20 is output to the aperture
region 111.
In this case, as shown in FIG. 6, the pyramid-shaped probe body 110
according to the present invention is constructed so that the
aspect ratio a0.times.b0 of one end on which an electromagnetic
wave is incident is greater than the aspect ratio a.times.b of the
other end thereof at which a near field is formed. Accordingly, the
probe body 110 is formed in a shape in which the width of each side
narrows toward the aperture 111 of the probe body 110.
At this time, the aspect ratio a0.times.b0 of one end of the probe
body 110 on which electromagnetic waves are incident is set to have
an area greater than the distribution of the electric field of the
electromagnetic waves so as to allow only an electromagnetic field
having a waveguide mode of TM.sub.00 to be output from the region
of the aperture 111. In this case, the aspect ratio a0.times.b0 of
one end is set to 400 nm.times.400 nm, while the aspect ratio
a.times.b of the other end is set to 40 nm.times.40 nm.
Therefore, as shown in FIGS. 10a and 10b, the diameter of a beam
spot 140 formed in the region of the aperture 111 of the probe body
110 is proportional to the total area obtained by adding the area
of the aperture (its aspect ratio is a.times.b) to the area of the
metal films symmetrically formed on both sides of the aperture.
Therefore, the diameter of the beam spot 140 formed in the region
of the aperture 111 is about 40 nm depending on the total area.
Further, the probe body 110 is made of a glass-related dielectric
member. When the electromagnetic waves are incident on the metal
films 120 symmetrically formed on both sides of the probe body 110
through the probe body 110, conditions allowing a surface plasmon
wave to propagate through the boundary surface between the probe
body 110 and the metal films 120 are satisfied.
The metal films 120 function to allow a surface plasmon wave formed
by the oscillation of charged particles excited on the surface
thereof in association with incident electromagnetic waves to
propagate in a direction of the aperture 111 of the probe body 110.
As shown in FIG. 7, the metal films 120 are coated on two
predetermined surfaces of four surfaces of the probe body 110 in a
thickness of about 15 nm while being spaced apart from each
other.
In this case, the metal films 120 are symmetrically formed on two
sides of the probe body 110 to allow the area of each metal film to
be smaller than that of each side of the probe body in such a way
that a conductive material, such as gold, silver or aluminum, is
coated to surround four sides of the pyramid-shaped probe body 110,
and an etching process is carried out with respect to the coated
conductive material.
In this case, the metal films 120 symmetrically formed on two sides
of the probe body 110 are constructed to have a shape narrowing
toward the aperture 111 of the probe body 110 due to the structural
characteristics of the probe body 110, as shown in FIG. 7.
Thereafter, the metal films 120 coated on the remaining two sides
of the probe body 110, in detail, the metal films 120 coated over
the range from a location, spaced apart from one end of the probe
body 110 on which electromagnetic waves are incident, to the other
end of the probe body 110, are eliminated through an etching
process.
The metal films 120 formed by the above-described process are
symmetrically coated on two sides of the probe body 110 while being
spaced apart from each other. Thereafter, if the surface plasmon
wave propagates through the surfaces of the metal films 120, a
predetermined potential difference is generated between the metal
films 120.
Therefore, the S/N ratio can be greatly improved by increasing the
surface plasmon wave propagating to the aperture 111 of the probe
body 110 due to the potential difference generated between the
metal films 120.
At this time, the surface plasmon wave is characterized in that it
propagates only through the surfaces of the metal films 120, not to
the inside or outside from the surface of the metal films 120.
Further, in order to form only a waveguide mode of TM.sub.00 in the
region of the aperture 111 of the probe body 110, an end of any one
metal film 120' of the metal films 120 may be eliminated from the
region of the aperture 111 of the probe body 110, as shown in FIG.
8.
That is, any one metal film 120' of the symmetrically coated metal
films 120 is formed on one side of the probe body 110 with the end
thereof being eliminated from the aperture region of the probe body
110, and the remaining metal film 120 is coated to the region of
the aperture 111 of the probe body 110.
At this time, since the metal film 120, coated to the region of the
aperture 111 of the probe body 110, propagates the surface plasmon
wave to form a near field in the region of the aperture 111 of the
probe body 110, a probe area corresponding to the eliminated metal
film 120' may be eliminated, as shown in FIGS. 10a and 10b, or the
probe area can be replaced and formed by air or another dielectric
medium 130 as shown in FIG. 9.
Therefore, the metal films 120, coated to the region of the
aperture 111 of the probe body 110, function as an aperture for
guiding the surface plasmon wave, so that the surface plasmon wave
propagates to the region of the aperture 111 of the probe body 110,
thus forming or changing a near field.
As described above, if the end of one of the metal films 120 is
eliminated, there is a disadvantage in that the surface plasmon
wave propagates only in one direction and energy transmitted
through the metal film 120 decreases by half, but there is a unique
advantage in that only a waveguide mode TM.sub.00 is formed in the
region of the aperture 111 of the probe body 110.
Further, the diameter of the beam spot 140 formed in the region of
the aperture 111 of the probe body 110 is proportional to the total
area obtained by adding the area of the aperture 111 (its aspect
ratio is a.times.b) to the area of the metal film formed on one
side of the aperture 111. Accordingly, a beam spot 140 formed in
the region of the aperture 111 depending on the total area has a
diameter smaller than that of the beam spot 140 shown in FIGS. 10a
and 10b, in detail, a diameter of about 30 nm.
Hereinafter, with reference to FIGS. 10a and 10b, an optical
recording and reproducing process using a pyramid-shaped near field
probe according to the present invention is described.
Referring to FIG. 11, an optical information recording and
reproducing apparatus 200 includes a laser diode 210 for emitting
laser light, an optical disc 220 for recording data using an
optical signal, an optical fiber 230 for guiding the laser light
emitted from the laser diode 210, a pyramid-shaped near field probe
100 for condensing the light guided through the optical fiber 230
and irradiating the condensed light on the optical disc 220, and a
lens 240 for condensing the laser light emitted from the laser
diode 210 and irradiating the condensed light onto the optical
fiber 230.
Further, the optical information recording and reproducing
apparatus 200 to which the present invention is applied includes a
beam splitter 250 for splitting light that is reflected in the
direction of the pyramid-shaped near field probe 100 by the optical
disc 220 and guided through the optical fiber 230, a photodetector
260 for converting an optical signal split by the beam splitter 250
into a current signal, and a signal reproduction unit 270 for
reproducing data recorded on the optical disc 220 using the current
signal detected by the photodetector 260.
In this case, the lens 240 is implemented in the form of a convex
lens for condensing the laser light emitted from the laser diode
210 on the optical fiber 230.
Further, the photodetector 260 is implemented with a photo diode
for converting an optical signal into a current signal.
The operation of the optical information recording and reproducing
apparatus having the above construction is described in detail.
First, a process of recording information on the optical disc 220
using an optical signal is described.
If laser light, a kind of electromagnetic wave to record
information on the optical disc 220, is emitted from the laser
diode 210, the laser light is condensed on the optical fiber 230
through the lens 240.
In this way, the laser light condensed by the lens 240 is guided
through the optical fiber 230 and propagates up to the
pyramid-shaped near field probe 100.
At this time, charged particles vibrate on the surfaces of the
metal films 120, forming the pyramid-shaped near field probe 100,
in association with the incident laser light, so that a surface
plasmon wave propagating through the surfaces of the metal films
120 is formed.
The surface plasmon wave formed by the above-described principles
propagates to the region of the aperture 111 of the probe body 110
through the boundary surface between the probe body 110 and the
metal films 120 that are symmetrically formed on both sides of the
probe body 110 while being spaced apart from each other, thus
influencing the near field formed in the region of the aperture 111
of the probe body 110.
In this case, when the surface plasmon wave propagates through the
surfaces of the metal films 120, a predetermined potential
difference is generated between the metal films 120, so that the
surface plasmon wave propagating to the region of the aperture 111
of the probe body 110 increases, thus remarkably improving the S/N
ratio.
As described above, the near field formed in the region of the
aperture 111 of the pyramid-shaped near-field probe 100 is used to
record data on the optical disc 220. In this case, light forming
the near field is irradiated to apply deformation to the optical
disc 220, thus recording data.
Since the data are recorded on the optical disc 220 through the
above-described process, it is easier to apply deformation to the
optical disc 220 and record data thereon as the amount of light
transmitted through the pyramid-shaped near field probe 100
increases. The reason for this is that, as the intensity of light
forming the near field increases, the optical disc 220 is more
easily deformed.
Further, since the width of the deformation on the optical disc 220
is determined in proportion to the size of the diameter of light
forming the near field, the amount of data to be recorded on the
optical disc 220 is determined depending on the diameter of the
near field formed in the region of the aperture 111 of the
pyramid-shaped near field probe body 110.
Therefore, in order to rapidly record a greater amount of data on
the optical disc 220, the present invention proposes the technology
of increasing transmissivity while minimizing the diameter of the
aperture 111 of the pyramid-shaped near field probe 100.
Next, a process of reading information recorded on the optical disc
220 through the above process is described.
If laser light is irradiated onto the optical disc 220 with various
pieces of information recorded thereon as described above, the
light irradiated onto the optical disc 220 is reflected in the
direction of the pyramid-shaped near field probe 100 and
transmitted to the lens 240 through the optical fiber 230.
In this case, the light guided through the optical fiber 230 is
condensed by the lens 240 and irradiated onto the beam splitter
250.
Further, when the beam splitter 250 splits the light irradiated by
the lens 240 and transmits the split light to the photodetector
260, the photodetector 260 detects an optical signal split by the
beam splitter 250, converts the optical signal into a current
signal, and outputs the current signal to the signal reproduction
unit 270.
The signal reproduction unit 270 reproduces data recorded on the
optical disc 220 using the current signal converted by the
photodetector 260 through the following process.
On the optical disc 220, portions, to which deformation is applied
and is not applied, exist to record data, so that the intensities
of light reflected by the two portions are different from each
other. Accordingly, the intensity of a current signal detected by
the photodetector 260 is also determined in proportion to the
intensity of light reflected by the optical disc 220.
As described above, since a difference is generated between the
intensities of current signals detected by the photodetector 260,
the signal reproduction unit 270 compares the intensity of the
current signal converted by the photodetector 260 with the
intensity of a preset reference signal, thus reproducing the
information recorded on the optical disc 220.
For example, if the current signal is greater than the reference
signal, the signal reproduction unit 270 recognizes the current
signal as "1", while if the current signal is less than the
reference signal, the signal reproduction unit 270 recognizes the
current signal as "0", thereby reproducing the information recorded
on the optical disc 220 in the form of a digital character.
As described above, the recorded data are read by allowing the
light transmitted through the pyramid-shaped near field probe 100
to be reflected by the optical disc 220. Accordingly, it is easier
to reproduce recorded information as the intensity of light
reflected by the optical disc 220 increases. In this case, the
intensity of light reflected by the optical disc 220 is
proportional to the intensity of light transmitted through the
pyramid-shaped near field probe 100.
Therefore, the present invention proposes the technology of
increasing the transmissivity of the pyramid-shaped near field
probe 100 to rapidly and precisely reproduce the information
recorded on the optical disc 220.
As described above, the present invention provides a pyramid-shaped
near field probe, which allows a surface plasmon wave to propagate
to the end of the probe through the metal films formed on both
sides of the pyramid-shaped probe body to form a near field, so
that optical efficiency increases at the end of the probe, thus
improving a Signal-to-Noise (S/N) ratio, and shortening the time
required to reproduce and record data.
Further, the present invention is advantageous in that the
pyramid-shaped near field probe is manufactured through a
semiconductor process, thus simplifying the manufacturing process
of the probe and improving the productivity thereof.
Although the preferred embodiments of the present invention have
been disclosed for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *